When you get an enemy down to 0 health, you're given a brief opportunity to attack for bonus experience. Combos don't seem to activate in this bonus mode. However, when I slash as fast as I can, I don't always get the same amount of bonus experience.

Is the bonus experience based on the number of attacks I complete? Is it based on the amount of damage I've dealt? Does technique make any difference, or is it all about speed and/or your attack attribute?